Rotary helical splined actuators have been employed in the past to achieve the advantage of high-output from a simple linear piston-and-cylinder drive arrangement. The actuator typically uses a cylindrical body with an elongated rotary shaft extending coaxially within the body, with an end portion of the shaft providing the drive output. An elongated piston sleeve has an outer sleeve portion splined to cooperate with corresponding splines on the body interior or a ring gear, and an inner sleeve portion splined to cooperate with corresponding splines on the shaft exterior. The piston sleeve is reciprocally mounted within the body with the shaft extending therewithin, and has a head for the application of fluid pressure to one or the other opposing sides thereof to produce axial movement of the piston sleeve.
As the piston sleeve linearly reciprocates in an axial direction within the body, the splines of the outer sleeve portion engage the splines of the body to cause rotation of the piston sleeve. The resulting linear and rotational movement of the piston sleeve is transmitted through the splines of the inner sleeve portion to the splines of the shaft to cause the shaft to rotate. Bearings are typically positioned interior of the body to rotatably support one or both ends of the shaft relative to the body.
While such an arrangement produces a relatively high-torque output, the capability of the actuator to support high moment loads and large axial and radial thrust loads has been limited. The actuator typically has a slender shaft with bearings between the shaft and end flanges or end caps of the body, with the bearings positioned radially inward of the body sidewall. It is desirable to use rotary actuators to rotate heavy loads and loads that produce large bending movements. For example, a rotary actuator may be used to rotate a large-diameter platform which extends radially far beyond the actuator body and which carries a crane, bucket lift or other mechanism having a boom reaching far outward of the platform. Once such arrangement is shown in the inventor's U.S. Pat. No. 4,508,016.
The conventional actuator is not well constructed to handle the high moments encountered when the shaft centrally supports a platform, since it does so in an almost needle point balanced arrangement. In such an arrangement, when the boom of the device carried by the platform is extended, the moments become extremely large and difficult for the conventional actuator shaft and shaft bearing configuration to handle. Further, the axial thrust loads encountered due to the weight of the platform, the crane, or other mechanism mounted thereon, and the workload it carries, are far too great for the conventional actuator shaft bearing configurations. Other uses of the actuator are envisioned which also subject the actuator shaft to high moments and large axial thrust loads, such as use to rotate a log grapple or to steerably turn the wheel assembly of a vehicle while supporting the weight of the vehicle above the wheel assembly.
A shortcoming of conventional actuators with bearings supporting the shaft at both ends of the body is that if a large bending load is transmitted through the shaft, such as when supporting a crane platform, any resulting radial movement or bowing of the shaft can cause the shaft, the piston sleeve and the ring gear to bind. This may inhibit operation of the actuator and damage the actuator. While increasing the size of the shaft and the bearings helps reduce the shaft movement and bowing that occurs under such loads, and hence the resulting binding, the result is a heavy and expensive actuator.
Another problem involves the cost of manufacturing actuators, especially ones designed to handle high moments and large axial and radial loads. In the past the actuator body has typically been designed with a thick wall construction, and since the bearing races are formed in the body sidewall of the actuator, the body must be hardened. The result is a heavy and expensive body. Even in lighter load applications where a thin-wall body construction is used, end caps with a plurality of the rods extending therebetween are often needed.
It will therefore be appreciated that there has long been a significant need for fluid-powered rotary actuators capable of handling increased moments and axial and radial shaft loads. The actuator should have a compact and lightweight design which allows use of a thin wall body construction without requiring use of tie rods. The actuator should be economical to manufacture. Preferably, the actuator should be able to operate even under large bending loads that produce some bowing of the shaft. The actuator should also permit preloading of the bearings which rotatably support the shaft with respect to the body without requiring disassembly of the actuator. Also, the actuator should provide for smooth start up and stopping action as the piston sleeve reaches its end limits of axial travel. Finally, the actuator should provide convenient means for attachment of hydraulic hoses that avoids twisting and damage of the hoses. The present invention fulfills these needs and further provides other related advantages.